The Ketogenic diet has long been known to be an effective therapy for intractable childhood epilepsy. However, its use has been limited by low palatability; between 85 and 90 percent of the total caloric intake has to be provided as dietary fat. Recently, medium chain triglycerides (a mixture of the triglycerides of octanoic and decanoic acids) have been found to induce ketosis more readily than do long chain (dietary) fats. A diet containing 60 percent of caloric needs as medium chain triglyceride (MCT) has been devised. The aim of the present study is to determine the long-term anticonvulsant effect and acceptability of the MCT diet in a group of children with refractory epilepsy. The effects of the MCT diet are compared with those of the standard 3:1 Ketogenic diet. The degree of ketosis induced by each diet is assessed by quantitative determinations of acetoacetate and beta-hydroxybutyrate in plasma. A search is made for an animal model in which an anticonvulsant effect of MCT can be demonstrated, to elucidate the mechanism of action of the MCT diet.